FIG. 1A of the drawings schematically shows a single-row light shutter array, which is taught in Japanese Provisional Patent Publication Nos. 60-159722 or 60-170828. The light shutter array consists of a series of shutter elements P.sub.1, P.sub.2, P.sub.3, . . . P.sub.n arranged in a single row and may be used in an electrooptical printer apparatus using a photo-sensitive drum (not shown). The shutter elements P.sub.1, P.sub.2, P.sub.3, . . . P.sub.n are located with respect to the drum so that a single-row pattern of pixels p.sub.1, p.sub.2, p.sub.3, . . . p.sub.n as shown in FIG. 1B may be projected onto the peripheral surface of the drum.
FIG. 2A shows an improved version of such a prior-art light shutter array which is experimentally fabricated in private by Applicant and is of the dual-row type consisting of two parallel rows of shutter elements, one row consisting of shutter elements P.sub.1, P.sub.2, P.sub.3, . . . P.sub.n and the other row consisting of shutter elements Q.sub.1, Q.sub.2, Q.sub.s, . . . Q.sub.n. The dual-row light shutter array as shown in FIG. 2A is advantageous over an array of the single-row type in that electrode segments can be easily connected to terminals of a control circuit with no consequent reduction in the resolving power. Only a set of alternative ones of the shutter elements is to be put to use with the other set of alternative shutter elements left out of use in each of the two rows so that, in effect, only the shutter elements which are located in staggering relationship between the two parallel rows may be selected for use. In the dual-row shutter element configuration shown in FIG. 2C, it is assumed that only the shutter elements P.sub.1, P.sub.3, . . . alternately arranged in the first row are to be put to use and, likewise, only the shutter elements Q.sub.2, Q.sub.4, . . . alternately arranged in the second row are to be put to use. The other set of alternately arranged shutter elements P.sub.2, P.sub.4, . . . of the first row and the other set of alternately arranged shutter elements Q.sub.1, Q.sub.3, . . . of the second row are left out of use.
Such a dual-row light shutter array may also be used in an electrooptical printer apparatus using a photo-sensitive drum (not shown). In this instance, the shutter elements selected out of the alternate shutter elements P.sub.1, P.sub.3, . . . of the first row are activated at a controlled timing and the shutter elements selected out of the alternate shutter elements Q.sub.2, Q.sub.4, . . . of the second row are activated at a predetermined time interval after the shutter elements of the first row have been activated. The photo-sensitive drum is driven for rotation at a speed selected so that beams of light passed through the selected ones of the shutter elements P.sub.1, P.sub.3, . . . of the first row and beams of light passed through the selected ones of the shutter elements Q.sub.2, Q.sub.4, . . . of the second row are allowed to reach the peripheral surface of the drum along a single line extending on the drum surface. The two rows of alternate shutter elements being activated with a predetermined time lag therebetween, a single-row pattern composed of the pixels p.sub.1, q.sub.2, p.sub.3, q.sub.4, . . . may thus be produced on the photo-sensitive drum of the printer apparatus as shown in FIG. 2B.
The single-row or dual-row light shutter array of the described type has a problem in that the single-row pattern of the pixels p.sub.1, p.sub.2, p.sub.3, . . . p.sub.n (FIG. 1B) or p.sub.1, q.sub.2, p.sub.3, q.sub.4, . . . (FIG. 2B) has gaps between the adjacent pixels produced on the photo-sensitive drum of the printer apparatus as will be seen from FIG. 1B or FIG. 2B. These gaps between the pixels produced on the drum have resulted from the gaps between the shutter elements of each of the rows in the light shutter array and result in recurring discontinuities in the generally linear pixel pattern. A pixel pattern with such discontinuities will significantly impair the aesthetic quality of the image to be printed or otherwise formed.
Another problem inherent in a conventional light shutter array of the described type is that a beam of light once admitted into a shutter element may be allowed out of the shutter element into another shutter element and cause a "crosstalk" between adjacent shutter elements of the light shutter array. An occurrence of such a crosstalk would impair the contrast of the images to be produced and is objectionable from the view point of producing an output image with a satisfactory degree of contrast.
In the meantime, a conventional light shutter array has generally been of the flat-electrode type which is coated with a control and lead electrode pattern applied to the surface of a PLZT substrate. Problems have however been encountered in a light shutter array of this flat-electrode type in that the device requires an unduly high driving voltage and may fail to operate properly due to a "crosstalk" which may occur between adjacent electrodes, and that the response characteristics of the device are rather insufficient.
With a view to obviating these problems, an advanced light shutter array has been proposed which has the individual shutter elements separated in block form from one another with a number of grooves cut into the substrate by the use of a mechanical cutting tool such as a dicing saw having a diamond cutter blade. Examples of a light shutter device of this type include the single-row shutter array disclosed in the named Japanese Provisional Patent Publication No. 61-38927 and the dual-row device which has been proposed by Applicant. Tests have been conducted with light shutter devices of these types to investigate into the optical performance characteristics of the devices. These tests have revealed that stresses are created in edge portions of the shutter elements when the grooves to separate the elements are being cut into the substrate. Such stresses remain throughout the use of the device and are responsible for the occurrence of leakage of light from the shutter elements even when the device is in an unbiased state. The leakage of light from the shutter elements causes reduction in the contrast of the resultant images and thus critically impairs the performance characteristics of the device.
It is, accordingly, an important object of the present invention to provide an improved electrooptical light shutter device having discrete shutter elements arranged so that the arrays of the shutter elements is capable of producing a fully continuous linear pixel pattern.
It is another important object of the present invention to provide an improved electrooptical light shutter device which features a light shutter array in which the possibility of a crosstalk occurring between adjacent shutter elements due to leakage of light from the array elements is minimized to enable the shutter device to produce an output image with a significantly enhanced degree of contrast which will provide an improved aesthetic quality of the image.
It is still another important object of the present invention to provide an improved electrooptical light shutter device in which leakage of light from edge portions shutter elements blocks is prevented in such a manner that a number of grooves are cut into the substrate with use of a mechanical cutting tool during fabrication of the light shutter array.
Yet, it is still another important object of the present invention to provide an optical printer apparatus using such an improved electrooptical light shutter device according to the present invention.